Well kind of a off the wall question, and not sure what you asking about. The Arduino software has commands that allow you to access (read or write) all the I/O pins one at a time at one command at a time. There is also a way to access I/O pins as 8 bit registers so you can read or write 8 I/O pins at a time.

If that doesn't answer your question, can you clarify what you wish to do with the I/O pins?

The digital pins are numbered 0-13, often called D0-D13. The analog pins are numbered 0-5 called A0-A5. The Arduino software knows that when you are using analog commands that the A0 to A5 pins are not the same pins as the digital pins D0 to D5.

To make it a little more confusing, one can, if you wish, to utilize the five analog pins as digital I/O pins by referring to them as pins 14-18.

These pin names and numbers are software definitions and the Arduino software does all the internal mapping to the actual physical pins.

use analog 0 as analog input and analog 1(digital 15) as digital input

Yes, of course.

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.Do not send technical questions via personal messaging - they will be ignored.I speak for myself, not Arduino.